Conventionally, a carrier-type catalyst composed of a heat resistant inorganic carrier carrying catalytically active component is generally used in a catalytic gas-phase oxidation reaction (partial oxidation reaction) for industrial purposes. Suitably used as such a carrier are materials that are stable thermally and chemically, that does not interfere with a reaction, and that does not react with the catalytically active component, and preferably materials that boast excellent heat conductivity so that the temperature in the reaction field can be maintained at a constant value by releasing reaction heat from the system.
Materials satisfying those conditions include self-sintering bodies of silicon carbide of a high purity which have been widely used as a carrier of a catalyst for practical uses. As examples, Japanese Laid-Open Patent Application No. 57-105241/1982 (Tokukaisho 57-105241) discloses the sintering bodies being suitably used as a carrier of a catalyst for synthesising phthalic anhydride from o-xylene or naphthalene, Japanese Laid-Open Patent Application No. 62-78/1987 (Tokukaisho 62-78) discloses a method of manufacturing maleic anhydride from benzene using a catalyst composed of the sintering body carrying catalytically active component, Japanese Laid-Open Patent Application No. 61-28456/1986 (Tokukaisho 61-28456) discloses a catalyst composed of the sintering body carrying catalytically active component as a catalyst for synthesising pyromellitic anhydride from 1,2,4,5-tetramethyl benzene, and Japanese Laid-Open Patent Application No. 64-63563/1989 (Tokukaisho 64-63563) discloses the sintering bodies being suitably used as a carrier of a catalyst for synthesising benzonitrile from toluene.
Nevertheless, since silicon carbide has a very high sintering temperature, a massive amount of energy, such as electricity, needs be used to produce a molded product that is a self-sintering body made by sintering. In addition, the sintering of silicon carbide needs be conducted under a non-oxidation atmosphere using an inert gas such as nitrogen gas. Therefore, those costs, including the electricity bill, add up and render the self-sintering of silicon carbide very expensive.
Incidentally, minerals such as steatite have a relatively low sintering temperature and can be sintered under an oxidation atmosphere. Self-sintering bodies of those minerals can be therefore manufactured at low costs. However, the self-sintering bodies of the minerals are inferior to the self-sintering body of silicon carbide in chemical stability and heat conductivity.
In light of the above fact, Japanese Laid-Open Patent Application No. 9-85096/1997 (Tokukaihei 9-85096) discloses a method of manufacturing a silicon-carbide-based inexpensive carrier, i.e., a carrier composed of silicon carbide along with silicon dioxide and mullite as inorganic binding component.
The carrier made from silicon carbide along with silicon dioxide and mullite as inorganic binding component exhibits excellent heat conductivity inherent to silicon carbide and can be formed into a molded product of a desired shape. However, such a carrier largely changes its properties over a period of time. So, conventional catalysts for catalytic oxidation use made from the carrier have a disadvantage of unstable catalytic activity over a period of time.